1. Field of the Invention
This invention relates to a power switching control apparatus, which is constituted to arrange phase switches at individual phases of a three-phase AC power circuit and to control the individual phase switches independently of one another.
2. Description of Related Art
A synchronous switching apparatus is disclosed in International Laid-Open WO000/04564. In this synchronous switching apparatus, phase switches arranged at the individual phases of a three-phase AC power circuit are controlled independently of one another, and the individual phase switches are so made at the set phases as to suppress the generation of the inrush current or surge voltage which is severe against the system device such as the transformer, shunt reactor, power lines or capacitor banks of the three-phase AC power circuit.
Generally speaking, however, the contacts of the phase switch are erroded by the arcs, and the drive mechanism of the moving contacts disperses and has its driving characteristics varied according to the surrounding environment such as the ambient temperature. JP2001-135205A has disclosed a one-phase power switching apparatus. In this power switching apparatus, on the basis of the waveform of a phase current and the pre-arcing time of a switch, the making operation time of the switch is detected and is reflected on the control of the next making instant of the switch. This making operation time of the switch is the action time from the time when the making command of the switch is fed to the time when the contact is actually connected.
In case the individual phase switches of the three-phase AC power circuit are made independently of one another and in set phases, no phase current flows in the state where the first phase switch is made, if the load is of a non-grounded neutral point type. In case the load is of the type, in which it has a common core of the grounded neutral point type, the phase switch to be finally made has two preceding phases made so that it is made in the substantial “0” voltage between contact. In the constitution where the making operation time of the phase switch is detected on the basis of the phase current waveform containing pre-arcs, therefore, the phase current waveforms containing the pre-arcs cannot be obtained when all the phase switches are made to raise a problem that it is impossible to detect the making operation times of all the phase switches precisely.